Alloy for hydrogen storage, method for absorption and release of hydrogen using the alloy, and hydrogen fuel cell using the method

ABSTRACT

A method for absorbing and releasing hydrogen comprises applying repeatedly hydrogen pressurization and depressurization to a hydrogen storage metal alloy of a body-centered cubic structure-type phase exerting a two-stage or inclined plateau characteristic in a hydrogen storage amount vs hydrogen pressure relation in an appropriate fashion to absorb and release hydrogen. At least at one stage during the release of hydrogen, the temperature (T 2 ) of the above-mentioned hydrogen storage metal alloy is made higher than the temperature (T 1 ) of the hydrogen storage metal alloy during the hydrogen absorption process (T 2 &gt;T 1 ). This enables the release and utilization of occluded hydrogen at a low-pressure plateau region or an inclined plateau lower region.

TECHNICAL FIELD

The present invention relates to a method for absorption and release ofhydrogen where a hydrogen storage metal alloy is repeatedly subjected topressurization and depressurization of hydrogen. In more detail, thepresent invention relates to a hydrogen storage metal alloy having atwo-stage plateau- or inclined plateau-property. Particularly, thepresent invention relates to a method for absorption and release ofhydrogen where the amount of released hydrogen increases withinpractical pressure ranges and temperature ranges, to a hydrogen storagemetal alloy suitable for such a method for absorption and release ofhydrogen and to a hydrogen fuel battery using the above method forabsorption and release of hydrogen.

RELATED ART OF THE INVENTION

At present, there have been worries not only about acid rain due to anincreasing NOx (nitrogen oxides) but also about global warming due to anincreasing C0 ₂ in association with an increase in consumption of fossilfuel such as petroleum and such environmental destruction has become aserious problem. Therefore, our attention has been greatly concentratedon development and practical application of various kinds of cleanenergy which is friendly to the earth. Part of means for developing sucha new energy is a practical application of hydrogen energy. Hydrogen isa constituent element of water inexhaustibly present on the earth andcan be not only produced using various kinds of primary energy but alsoutilized as fluid energy in place of conventionally used petroleumwithout the risk of destroying the environment because its product ofcombustion is only water. In addition, unlike electricity, it hasexcellent characteristics such as its relatively easy storage.

In recent years, therefore, investigation has been actively conductedinvolving hydrogen storage metal alloys as media for storing andtransporting hydrogen and their practical application has been expected.Such hydrogen storage metal alloys are metals/alloys which can absorband release the hydrogen under an appropriate condition and, by the useof such alloys, it is possible to store the hydrogen not only at lowerpressure but also at higher density as compared to the case of theconventional hydrogen cylinders. In addition, the hydrogen volumedensity thereof is nearly equal to or rather greater than that of liquidor solid hydrogen.

These hydrogen storage metal alloys which have been chiefly investigatedare, for example, those alloys which each have a body-centered cubic(hereinafter, referred to as “BCC”) structure, including V, Nb, Ta orCr—Ti—Mn alloys, Cr—Ti—V alloys, etc. as proposed in Japanese UnexaminedPatent Publication (Kokai) No. 10-110225 (JP, A, 10-110225). It has beenknown that those alloys adsorb and store hydrogen in greater quantitiesas compared with AB₅ alloys such as LaNi₅ and AB₂ alloys such as TiMn₂which have been practically used until now. This is because the numberof hydrogen absorbing sites in the crystal lattice is great in the BCCstructure and the hydrogen absorbing capacity is as large as H/M=ca. 2wherein H is occluded hydrogen and M is a constituent element for thealloy (about 4.0 wt % in alloys of V, etc. having an atomic weight ofaround 50), being extremely large.

It has been known that such a BCC alloy having a relatively largehydrogen absorbing capacity conducts a two-step reaction during thecourse of its absorbing hydrogen to form a hydride, as shown in Reillyand R. H. Wiswall, Inorg. Chem., 9 (1970), 1678). For example, V reactswith hydrogen at ambient temperature and forms two kinds of hydridesdepending upon the pressure of hydrogen. At first, at the initialreaction stage wherein hydrogen pressure is low, a very stable hydrideis formed as V→VH_(0.8) (α phase→β phase) (hereinafter, referred to as“low-pressure plateau part”) and, at around room temperature, a reversereaction thereof rarely happens. When further more hydrogen pressure isapplied, a hydride is formed as VH_(0.8)→VH_(2.01)(β phase→γ phase;referred to as “high-pressure plateau part”). The equilibrium hydrogenpressure of this reaction is appropriate (approximately a fewatmospheric pressure at around room temperature). Therefore, suchV-containing BCC alloys have been briskly studied as high-capacityhydrogen storage metal alloys.

FIG. 1 is a conceptional chart of a PCT curve of a single substance Vhaving a two-stage plateau comprised of the aforementioned low-plateauand high-plateau parts. The flat region at the hydrogen pressure of 10⁻¹Pa in FIG. 1 is a low-pressure plateau part and the flat region at thehydrogen pressure of 10⁶ Pa is a high-pressure plateau part. Theinclined region between the low-pressure plateau part and thehigh-pressure plateau part is a region complying with Sieverts's law.Besides V, an example of the metal having such a two-stage plateau is Nb(low-pressure phase: NbH, high-pressure phase: NbH₂). In addition, Tishows a two-stage plateau by a transformation of α→β→γ although itoperates at elevated temperature. An intermetallic compound having atwo-stage plateau includes FeTi which works at near 40° C. Further,alloys such as (Zr, Ti)V₂ show an inclined plateau and those alloys arealso used as hydrogen storage metal alloys.

Examples of the prior art techniques presumably based upon the idea ofdeveloping a high-capacity hydrogen storage metal alloy relying on theabove-mentioned two-stage plateau and inclined plateau characteristicsare as follows:

(a) spinodal decomposition tissues are expressed in a body-centeredcubic structure Ti alloy (the above JP, A, 10-110225);

(b) a Ti—Cr—V alloy is admixed with Cu and/or rareearth elements (theabove JP, B2, 4-77061);

(c) a Ti alloy melt is rapidly cooled to form a BCC mono phase at roomtemperature (Japanese Unexamined Patent Publication (Kokai) No.10-158755 (JP, A, 10-158755)); and

(d) a BCC alloy comprised as main elements of Ti—Cr is adjusted for itslattice constant (Japanese Unexamined Patent Publication (Kokai) No.07-252560 (JP, A, 07-252560)).

Among the above-mentioned methods for absorbing and releasing hydrogen,those where temperature for absorption and desorption of hydrogen ismentioned are JP, A, 10-110225 and JP, A, 07-252560, both which disclosethe methods where hydrogen is absorbed and released at a constanttemperature, provided that, in the latter JP, A, 07-252560, theactivating pretreatment is carried out by means of a two-stage treatmentcomprising a low temperature in the former stage and a high temperaturein the latter stage while the temperature for hydrogen absorption anddesorption is constant (20° C.). In Japanese Patent Publication No.59/38293 (JP, B2, 59/38293), hydrogen is absorbed with a hexagonalTi—Cr—V type alloy which is not a BCC alloy and a method of heating at100° C. or higher (lines 32 to 39, column 4) is for absorbing andreleasing hydrogen at a constant temperature as well.

However, in the hydrogen storage metal alloy having the above-mentionedtwo-stage plateau characteristic such as V-containing BCC alloy whichhas been often investigated as the high-capacity hydrogen storage metalalloy, the hydrogen-absorbing reaction at the low-pressure plateauregion proceeds only to the side of the reaction with hydrogen at roomtemperature. Therefore, it has not been carried out in the prior artthat the hydrogen occluded is taken out in such a low-pressure plateauregion and used as an effective hydrogen.

Thus, in the above-mentioned JP, A, 10-110225 and JP, B2, 4-77061, sucha low-pressure plateau region is not referred to. In the latter patent,since there is a teaching that the production of TiH₂ (high-pressureplateau region compound) is to be avoided, only the hydrogen-absorbingreaction between the low-pressure plateau region and the high-pressureplateau region is utilized.

It is said that, in general, the amount of hydrogen taken out from abody-centered cubic structure type hydrogen storage metal alloy such aspure V and pure Nb is very low as compared with the theoretical amount(Hydrogen Storage Metal Alloy—Physical Properties and Applications, NewEdition, by Yasuaki Osumi, published by Agne Technique Center, Japan,first printing of the first edition issued on Oct. 30, 1993, page 309).

In AB₅ alloys such as LaNi₅ or BCC alloys, which have been practicallyutilized up to now, it is possible to control the equilibrium pressureregarding reaction with hydrogen by controlling the alloy components. Itis also possible that the equilibrium pressure of the hydrogen storagemetal alloy with hydrogen is controlled by the operating temperature.However, the conventional research on alloys as such is not particularlybased on consciousness of improvement in the hydrogen-absorbingcharacteristic at the above-mentioned low-pressures plateau region.

Accordingly, it is believed that, in order to increase the hydrogenabsorption capacity in the aforementioned BCC type hydrogen storagemetal alloy, it is effective that the hydrogen in the reaction of aphase→β phase, i.e., the reaction at the low-pressure plateau part (forexample, the reaction of V→VH_(0.8) in the case of V), contributes tothe reaction of absorption and desorption in addition to the β-phaseregion of the BCC type alloy (a portion complying with a Sieverts's lawbetween a low-pressure plateau region and a high-pressure plateauregion). However, such a means has not been disclosed yet.

Accordingly, an object of the present invention is, with regard to theconventional pure V or pure Nb showing a two-stage plateau or inclinedplateau region or BCC solid solution alloys including not only solidsolutions showing a hydrogen absorption/desorption reaction similar tothe above-mentioned metal, but also Ti—Cr system alloys, etc., toprovide a hydrogen storage metal alloy in which the hydrogen not onlybetween α phase→β phase, i.e. in the reaction at the low-pressureplateau region but also at a low-pressure β phase region (a low-pressureregion showing a behavior similar to a Sieverts's law between alow-pressure plateau region and a high-pressure plateau region) is madecontributed in an absorption/desorption reaction of hydrogen in areversible manner so that much more amounts of hydrogen can be absorbedand released and also to provide not only a method for absorbing andreleasing hydrogen with the said alloy but also a hydrogen fuel batteryusing the said method.

SUMMARY OF THE INVENTION

In order to achieve the aforementioned objects, the present inventionprovides a novel hydrogen storage metal alloy. According to the presentinvention, the novel hydrogen storage metal alloy has the followingcharacteristics:

(1) it has as its main phase a body-centered cubic structure-type phaseexerting a two-stage or inclined plateau characteristic in a hydrogenstorage amount vs hydrogen pressure relation, and

(2) the composition ratio of constituent metals for the alloy isadjusted to an appropriate range in order to reduce the stability of thehydrogen occluded in the alloy during the low-pressure plateau region orthe lower plateau region of the inclined plateau such that an alloytemperature (T2) during at least a period in a hydrogen release processcan be brought to higher than an alloy temperature (T1) in ahydrogen-absorption process (T2>T1) whereby at least part of theoccluded hydrogen will be made desorbable during the low-pressureplateau region in the above-mentioned two-stage plateau or the lowerplateau region of the inclined plateau.

Such characteristics lead to the following:

the occluded hydrogen can be unstabilized in the alloy so that the alloytemperature may be brought to high (T2) during the hydrogen desorptionprocess, thereby facilitating the release of hydrogen during theaforementioned low-pressure plateau region or the lower plateau regionof the inclined plateau region, and therefore the occluded hydrogen atthe low-pressure plateau region or the lower plateau region of theinclined plateau region, which has been neither desorbed nor utilized atall, can be taken out as utilizable hydrogen, with the result that theamount of the utilizable hydrogen in such a hydrogen storage metal alloywill be increased.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those wherein the alloy temperature (T1) during thehydrogen-absorbing process may range from the extremely low temperaturein the living areas on the earth to 373 K.

As a result thereof, the alloy temperature (T1) during thehydrogen-absorbing process can be made near an ambient temperatureregion whereby the practicability can be improved.

It is preferred that the hydrogen storage metal alloys of the presentinvention are V alloys which each not only have a suitably adjustedcomposition to reduce the stability of the occluded hydrogen asaforementioned but also contain 0 to 95 at % of at least one or moremembers selected from the group consisting of Nb, Ta, W, Mo, Ti, Cr, Mn,Fe, Al, B, Co, Cu, Ge, Ni and Si.

As a result thereof, the alloys each having such a composition arehighly effective in unstabilizing the occluded hydrogen therein andtherefore suitable for releasing a large amount of hydrogen therefromduring the low-pressure plateau region or the lower plateau region ofthe inclined plateau by raising the alloy temperature during ahydrogen-desorbing process.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those alloys which each have not only a suitably adjustedcomposition to reduce the stability of the occluded hydrogen asaforementioned but also a fundamental composition of the formula:

V_(a)Ti_((41−0.4a+b))Cr_((59−0.6a−b))

wherein 0≦a≦70 at % and −10≦b≦10 at %.

As a result thereof, the alloys each having such a composition canocclude a large amount of hydrogen at the high-pressure plateau regionand are greatly effective in unstabilizing the occluded hydrogentherein. Therefore, such alloys are preferable to release a largequantity of occluded hydrogen during the low-pressure plateau region orthe lower plateau region of the inclined plateau by raising the alloytemperature during the hydrogen-desorbing process and have an effectiveamount of utilizable hydrogen in great quantities, thereby giving a highpracticability.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those alloys which each have not only a suitably adjustedcomposition to reduce the stability of the occluded hydrogen asaforementioned but also a fundamental composition of the formula:

V_((a−d))M2_(d)Ti_((41−0.4a+b))Cr_((59−0.6a−b−c))M_(c)

wherein 0≦a≦70 at %, −10≦b≦10+c, 0≦c, 0≦d≦a, M is at least one or moremembers selected from the group consisting of Nb, Mo, Ta, W, Mn, Fe, Al,B, C, Co, Cu, Ge, Ln (various lanthanoid metals), N, Ni, P and Si, andM2 is at least one or more members selected from the group consisting ofMo, Nb, Ta, W, Mn, Fe and Al.

As a result thereof, the alloys each having such a composition canocclude a large amount of hydrogen at the high-pressure plateau regionand are greatly effective in unstabilizing the occluded hydrogentherein. Therefore, such alloys are preferable to release a largequantity of occluded hydrogen during the low-pressure plateau region orthe lower plateau region of the inclined plateau by raising the alloytemperature during the hydrogen-desorbing process and have an effectiveamount of utilizable hydrogen in great quantities, thereby giving a highpracticability. In addition, as a result of suitable admixture with atleast one or more elements selected from the above-mentioned lanthanoidmetals, N, Ni, P and Si, it is achievable to lower the melting point ofthe alloy and to improve the flatness of the plateau resulted thereby,and it is possible to either free the alloy of a heating treatment whichis apt to cause a spinodal decomposition or shorten a heating treatmenttime, thereby leading to an effect that a decrease in the hydrogenstorage amount can be suppressed.

It is preferred that the hydrogen storage metal alloys according to thepresent invention are those wherein the tissue structure of theabove-mentioned suitably adjusted hydrogen storage metal alloy is of abody-centered cubic structure mono phase without any spinodaldecomposition phase or has a body-centered cubic structure together withonly a minimum spinodal decomposition phase which is unavoidablyproduced.

As a result thereof, the hydrogen storage metal alloy has a minimumspinodal decomposition phase or has no spinodal decomposition phase,thereby enabling a decrease in hydrogen adsorption capacity due to theformation of spinodal decomposition phase to be suppressed as little aspossible.

A method for absorbing and releasing hydrogen by using the hydrogenstorage metal alloy according to the present invention comprises:

applying repeatedly hydrogen pressurization and depressurization to thehydrogen storage metal alloy of a body-centered cubic structure-typephase exerting a two-stage or inclined plateau characteristic in ahydrogen storage amount vs hydrogen pressure relation in an appropriatefashion to absorb and release hydrogen, and at least at one stage duringthe release of hydrogen, making the temperature (T2) of theabove-mentioned hydrogen storage metal alloy higher than the temperature(T1) of the hydrogen storage metal alloy during the hydrogen absorptionprocess (T2>T1).

Such characteristics lead to the following: it is now possible to takeout as a utilizable hydrogen the occluded hydrogen at the low-pressureplateau region or the lower plateau region of the inclined plateau whichhas not been desorbed and utilized at all whereby the amount ofutilizable hydrogen can be increased in the hydrogen storage metalalloy.

It is preferred that the alloy temperature (T1) during the abovehydrogen-absorbing process is within a range of from the extremely lowtemperature in the living areas on the earth to 373 K in the method forabsorbing and releasing hydrogen by using the hydrogen storage metalalloy according to the present invention.

As a result thereof, the alloy temperature (T1) during thehydrogen-absorbing process can be made near an ambient temperatureregion whereby the practicability can be improved.

It is preferred that the method for absorbing and releasing hydrogenaccording to the present invention comprises using a hydrogen storagemetal alloy wherein the composition ratio of the constituent metals forthe alloy is adjusted to an appropriate range in order to reduce thestability of the hydrogen occluded in the alloy during either thelow-pressure plateau region or the lower plateau region of the inclinedplateau such that the temperature of the said alloy can be brought tothe above high temperature (T2) whereby at least part of the occludedhydrogen will be made desorbable during either the low-pressure plateauregion in the above-mentioned two-stage plateau or the lower plateauregion of the inclined plateau.

As a result thereof, the occluded hydrogen can be unstabilized in thealloy, thereby facilitating the release of hydrogen from either theabove low-pressure plateau region or the lower plateau region of theinclined plateau when the temperature of the said alloy is made higher(T2) during the hydrogen release process, with the result that theamount of effective hydrogen can be increased.

It is preferred that the method for absorbing and releasing hydrogenaccording to the present invention comprises using a hydrogen storagemetal alloy wherein the aforementioned adjustment is in such a mannerthat the composition ratio of the constituent metals for the alloy isadjusted suitably so as to reduce the stability of the occluded hydrogenin the alloy within either the low-pressure plateau region or the lowerplateau region of the inclined plateau.

It is preferred that the method for absorbing and releasing hydrogenaccording to the present invention comprises using a hydrogen storagemetal alloy with a suitably adjusted composition to reduce the stabilityof the above occluded hydrogen, said hydrogen storage metal alloy beinga V alloy containing 0 to 95 at % of at least one or more membersselected from the group consisting of Nb, Ta, W, Mo, Ti, Cr, Mn, Fe, Al,B, Co, Cu, Ge, Ni and Si.

As a result thereof, the alloy having such a composition is highlyeffective in unstabilizing the occluded hydrogen therein and thereforesuitable for releasing a great deal of hydrogen from the low-pressureplateau region or the lower plateau region of the inclined plateau byraising the alloy temperature during the hydrogen release process.

It is preferred that the method for absorbing and releasing hydrogenaccording to the present invention comprises using a hydrogen storagemetal alloy with a suitably adjusted composition to reduce the stabilityof the above occluded hydrogen, said hydrogen storage metal alloy havinga fundamental composition of the formula:

 V_(a)Ti_((41−0.4+b))Cr_((59−0.6a−b))

wherein 0≦a≦70 at % and −10≦b≦10 at %.

As a result thereof, the alloy having such a composition has not only agreat deal of occluded hydrogen therein at the high-pressure plateauregion but also a high activity in unstabilizing the hydrogen occludedin the alloy. Therefore, such alloys are suitable for releasing a greatdeal of hydrogen from the low-pressure plateau region or the lowerplateau region of inclined plateau by raising the alloy temperatureduring the hydrogen release process and highly practicable because agreat amount of effective hydrogen is utilizable therein.

It is preferred that the method for absorbing and releasing hydrogenaccording to the present invention comprises using a hydrogen storagemetal alloy with a suitably adjusted composition to reduce the stabilityof the above occluded hydrogen, said hydrogen storage metal alloy havinga fundamental composition of the formula:

V_((a+b))M2_(d)Ti_((41−0.4a+b))M_(c)

wherein 0≦a≦70 at %, −10≦b≦10+c, 0≦c, 0≦d≦a, M is at least one or moremembers selected from the group consisting of Nb, Mo, Ta, W, Mn, Fe, Al,B, C, Co, Cu, Ge, Ln (various lanthanoid metals), N, Ni, P and Si, andM2 is at least one or more members selected from the group consisting ofMo, Nb, Ta, W, Fe and Al.

As a result thereof, the alloy having such a composition has not only agreat deal of occluded hydrogen at the high-pressure plateau region butalso a high activity in unstabilizing the hydrogen occluded in thealloy. Therefore, such alloys are suitable for releasing a great deal ofhydrogen from the low-pressure plateau region or the lower plateauregion of inclined plateau by raising the alloy temperature during thehydrogen release process and highly practicable because a great amountof effective hydrogen is utilizable therein.

In addition, the suitable admixture with at least one or more elementsselected from the group consisting of the above-mentioned lanthanoidmetals, N, Ni, P and Si leads to a decrease in the melting point of thealloy and an improvement in the flatness of the plateau resulted therebywhereupon the resultant alloy products are successful in suppressing adecrease in hydrogen adsorption capacity because a heating treatmentwhich is apt to cause a spinodal decomposition is not applied or atreating time is shortened.

It is preferred that the method for absorbing and releasing hydrogenaccording to the present invention comprises using a hydrogen storagemetal alloy wherein the tissue structure of the aforementioned suitablyadjusted hydrogen storage metal alloy is of a body-centered cubicstructure mono phase without any spinodal decomposition phase or has abody-centered cubic structure together with only a minimum spinodaldecomposition phase which is unavoidably produced.

As a result thereof, the hydrogen storage metal alloy has a minimumspinodal decomposition phase or has no spinodal decomposition phase.Therefore, a reduction in the amount of occluded hydrogen by theformation of spinodal decomposition phase can be suppressed as little aspossible.

The hydrogen fuel battery of the present invention is characterized inthat the battery is equipped with

a hydrogen storage tank including a hydrogen storage metal alloy,

a temperature controlling means whereby the above hydrogen storage metalalloy is directly heated or cooled or the atmospheric temperature of thesaid hydrogen storage metal alloy is raised or cooled,

a fuel battery cell in which hydrogen supplied from the said hydrogenstorage tank can be subjected to a chemical change to output an electricpower, and

a controller where a control is done in such a manner that, with regardto the temperature (T1) of the above hydrogen storage metal alloy duringthe stage of hydrogen absorption, the temperature of the said alloyduring at least one period during the release of hydrogen is made higher(T2) than the temperature (T1) thereof during the abovehydrogen-absorbing process.

Such characteristics lead to the following: during the hydrogen releasethe temperature (T2) of the aforementioned hydrogen storage metal alloycan be made higher than the temperature (T1) during thehydrogen-absorbing process whereby it is now possible to take out as autilizable hydrogen the occluded hydrogen at the low-pressure plateauregion or at the lower plateau region of the inclined plateau, saidoccluded hydrogen which has been neither desorbed from the hydrogenstorage metal alloy nor utilized before, and to increase electric energyobtained by the fuel battery cell.

For the hydrogen fuel battery of the present invention, it is preferredthat the aforementioned controller is capable of appropriatelycontrolling a pressure, temperature and flow rate of the hydrogen gassupplied from the above-mentioned hydrogen storage tank to theabove-mentioned fuel battery cell.

As a result thereof, the pressure, temperature and flow rate of hydrogengas can be controlled whereby it is possible to control amounts ofgenerated electric energy in the fuel battery cell appropriatelydepending upon the load and to enhance the utilizing efficiency of thehydrogen used in the said fuel battery cell.

For the hydrogen fuel battery of the present invention, it is preferredthat the above-mentioned temperature controlling means is arranged so asto enable the heat discharged from the above-mentioned fuel battery cellor the exhaust gas discharged from the said fuel battery cell to beutilized for the above-mentioned heating.

As a result thereof, the discharged heat or the exhausted heat of thefuel battery cell can be utilized for raising the temperature of theabove-mentioned hydrogen storage metal alloy whereby no electric energyor the like is necessary for raising the temperature of such a hydrogenstorage metal alloy and the efficiency throughout the hydrogen fuelbattery can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptional diagram of a PCT curve of metal V.

FIG. 2 is a graph showing a typical relation between a hydrogenabsorption-dissociation curve and temperature in LaNi₅, etc.

FIG. 3 is a graph showing amounts of released hydrogen depending on therise in the temperature upon hydrogen release in LaNi₅ , etc.

FIG. 4 is a graph showing a hydrogen absorption characteristic (313 K)of V_(x)—Ti_((40−0.4x))—Cr_((60−0.6x)) cast alloy.

FIG. 5 is a graph showing a hydrogen absorption characteristic under theordinary cycle in a heat-treated V_(x)—Ti_(37.5)—Cr_((62.5−x)) alloy.

FIG. 6 is a graph showing an influence of the measuring temperature on ahydrogen absorption characteristic in a V₇₀Zr_(0.5)Ti_(11.5)Cr₁₈ alloy

FIG. 7 is a graph showing a hydrogen absorption and desorptioncharacteristic when the measuring temperature is 303 K and 323 K in aV₇₀Zr_(0.5)Ti_(11.5)Cr₁₈ alloy.

FIG. 8 is a graph (conceptional diagram) showing an influence of thetemperature difference in a PCT curve having a two-stage plateau.

FIG. 9 is a graph (conceptional diagram) showing a volume increase ofthe temperature difference in a PCT curve having a two-stage plateau.

FIG. 10 is a graph showing the hydrogen absorption-desorptioncharacteristic obtained by conducting an ordinary absorption-desorptioncycle (the second cycle) and a cycle according to the method of thepresent invention (the third cycle) for a V₄₀Ti₂₅Cr₃₅ alloy.

FIG. 11 is a graph showing a hydrogen absorption-desorptioncharacteristic when the measuring temperature is 313 K in a V₃₀Ti₃₀Cr₄₀alloy.

FIG. 12 is a graph showing a hydrogen absorption-desorptioncharacteristic obtained by conducting the fourth and the fifth cyclesafter the absorption-desorption cycle conducted in FIG. 11.

FIG. 13 is a graph showing a hydrogen absorption characteristic in thethird cycle of a V₃₅Ti₂₅Cr₄₀ alloy subjected to a heating treatment at1573 K for a given time.

FIG. 14 is a graph showing hydrogen absorption characteristics at 368 Kof a V_(x)Ti₃₀Cr_((70−x)) alloy (X=27.5, 30, or 32.5).

FIG. 15 is a graph showing a hydrogen absorption characteristic at 313 Kof a V_(27.5)Ti₃₀Cr_(42.5) alloy.

FIG. 16 is a graph showing an effective hydrogen absorptioncharacteristic when the method of the present invention is applied to aV_(27.5)Ti₃₀Cr_(42.5) alloy.

FIG. 17 is a graph showing a conceptional proof (upon hydrogen release;raised from 313 K to 368 K, and dissociation pressure controlled) of thedifferential temperature method using a V₂₀Ti₃₅Cr₄₅ sample.

FIG. 18 is a graph showing a hydrogen absorption characteristic when thealloy working method of the present invention is applied to aV_(x)—Ti_((40−0.4x))—Cr_((60−0.6x)) cast alloy which is an alloyaccording to the present invention.

FIG. 19 is a hydrogen absorption characteristic graph showing aninfluence of a temperature rise on dissociation pressure in aV₄₀Nb₃Ti₂₅Cr₃₂ alloy.

FIG. 20 is a graph showing a hydrogen absorption characteristic when thedifferential temperature method of the present invention is applied to aheat-treated V_(x)—Ti_(37.5)—Cr_((62.5−x)) alloy.

FIG. 21 is a system flow chart showing an embodiment of the hydrogenfuel battery according to the present invention.

FIG. 22 is a schematic chart showing a mechanism of generation ofelectric power in the fuel battery cell used in the hydrogen fuelbattery of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As hereunder, the present invention will be illustrated by referring tothe drawings.

First, the reason why the composition of the alloy according to thepresent invention is defined as above is that a reaction of V→VH_(0.8)(α→β phase) in pure V is very stable and it is difficult to dissociatehydrogen from VH_(0.8) under a practical condition but, when it is keptin vacuo at 673 K (300° C.) for example, it is possible to dehydrogenateit. In the inventive alloy wherein V is greatly substituted with Ti andCr, stability of V(M)H_(0.8) (“V(M)” refers to a solid solution of V) islowered whereby hydrogen is made easily dissociated even at therelatively low practical temperature. Although the alloy of the presentinvention is in a composition where a spinodal decomposition is apt totake place, it is concluded to be allowed within an extent of beingunavoidably formed because, as will be mentioned later in detail, aspinodal decomposition tissue is a source of deterioration of a hydrogenabsorption characteristic.

Then the reason for selecting the compositions of the alloy according tothe present invention will be explained. Thus, V is capable of forming aBCC mono phase within a composition range of 5 to 100 at %. Further, Tiand Cr are the elements which lower the stability of VH_(0.8) when madeinto an alloy with V. The atomic radius of Ti (1.47Å) is bigger thanthat of V (1.34Å) and that of Cr (1.30Å). Therefore, when V issubstituted with Ti and Cr and an amount of substituent Ti is more thanthat of substituent Cr, a lattice constant of the BCC main phase becomesbig whereby a plateau pressure of a PCT curve lowers. In the alloy ofthe present invention, V is greatly substituted with Ti and Cr so as tolessen the stability of V(M)H_(0.8) formed at the above-mentioned lowerpressure plateau is lowered, thereby aiming at increasing an amount ofreleased hydrogen from the said alloy. However, the hydrogendissociation pressure at the high-pressure plateau region is to be keptwithin a practical range and, for such a purpose, the substitution ratioof Ti and Cr in the substitution with Ti and Cr as mentioned above comesto an important factor.

The starting composition in the present invention is V₇₀Ti₁₂Cr₁₈(figures are in atomic %). This alloy is a substance derived from pure Vby substituting 30 at % of V with 12 at % of Ti and 18 at % of Cr; inother words, wherein 30 at % of V has been replaced therewith at a ratioof Ti:Cr=4:6. When the total amount of V was replaced therewith at aratio of Ti:Cr=4:6, an alloy of Ti₄₀Cr₆₀ was produced. In order tosuitably adjust pressure conditions, a fundamental composition of theformula:

V_(a)Ti_((41−4a))Cr_((59−0.6a))

wherein a is an atomic % of V in the alloy, is derived for thecomposition wherein V is 0 at % in a Ti₄₁Cr₅₉ alloy and the range of afalls within 0≦a≦70 at %.

FIG. 4 shows a hydrogen absorption characteristic of aV_(x)—Ti_((40−0.4x))—Cr_((60−0.6x)) cast alloy at 313 K (40° C.). It isunderstood that the alloy wherein the level of V has been made less than80 at % shows a good characteristic.

In order to allow the dissociation pressure of the alloy to take anappropriate range (in other words, to adjust it depending upon theoperating temperature), the term b is set to give an extent for theselection of alloy components so as to enable the dissociation pressureto be adjusted to some extent and −10≦b≦10 at % is basic.

FIG. 5 shows a hydrogen absorption characteristic (the third cycle) at313 K (40° C.) of the heat-treated alloy which was produced bysubjecting a

V_(x) 13 Ti_(37.5)—Cr_((62.5−x))

alloy (X=0 to 7.5) to a heating treatment for 1 hour at 1673 K (1400°C.). It is understood from the drawing that its hydrogen absorptioncapacity comes to as high as 2.8 mass % when a BCC structure is presentby application of a heating treatment even when the level of V in thealloy is as small as 5 to 7.5 atomic %.

Further, in case the Cr component among the alloy components issubstituted with other components, when the substituent is M in thealloy and the amount of substituents is c-at %, the basic formula is

V_(a)Ti_((41−0.4a+b))Cr_((59−0.6a−b−c))M_(c).

Since there is a tendency that a dissociation pressure increases by acomponent M, a condition for b is introduced to be −10≦b≦10+c-at %. Thisalloy may also be subjected to a hydrogen absorption/desorption at apredetermined temperature like in the conventional case. Although onlyabout one-half of theoretical amount of hydrogen can be taken out in thecase of the conventional alloys, there is an advantage in the alloy ofthe present invention that a great increase in hydrogen desorptioncapacity is achieved.

As shown in FIG. 5, it is understood that the BCC type V—Ti—Cr systemalloy containing a micro amount of V has a high hydrogen storagecapacity. It has been known that the element which is apt to form a BCCstructure with Ti and Cr, like V, is Mo, Nb, Ta, W, Fe or Al. To aim ata BCC type structure by substituting part of V with such an element isbelieved to be effective from a phase diagram (the component capable ofaccelerating the BCC formation will be hereinafter referred to as an M2term). In case where the V term among the alloy components is replacedwith the above M2 term, an amount of the substitient M2 is defined asd-at % (0≦d≦a) wherein the M2 component may also be utilized as theabove-mentioned substituent term for Cr, i.e., the M term.

The hydrogen storage metal alloy according to the present inventionprovided as such is characterized in that the alloy is a hydrogenstorage V type metal alloy having a two-stage plateau characteristic,and has a composition of the following formula:

V_((a−d))M2_(d)Ti_((41−0.4a+b))Cr_((59−0.6a−b−c))M_(c)

wherein 0≦a≦70 at %, −10≦b≦10+c, 0≦d ≦a, M is at least one or moreelements selected from the group consisting of Nb, Mo, Ta, W, Mn, Fe,Al, B, C, Co, Cu, Ge, Ln (various lanthanoid metals), N, Ni, P and Si,and M2 is at least one or more elements selected from the groupconsisting of Mo, Nb, Ta, W, Mn, Fe and Al, and the main phase of thealloy is in a body-centered cubic structure and do not have a spinodaldecomposition tissue or has a spinodal decomposition phase which isunavoidably produced.

The method of the present invention is a method for effectivelyutilizing the occluded hydrogen in a low-pressure plateau region ofhydrogen storage metal alloy showing a two-stage plateau or inclinedplateau characteristic which comprises:

absorbing hydrogen at a low temperature region (T1),

elevating a temperature during a hydrogen release process, and

increasing a hydrogen dissociation pressure of the low-pressure plateauregion at an elevated temperature region (T2≦T1) whereby the hydrogen atthe low-pressure plateau region is released.

The lowest limit in the above low-temperature region (T1) is anextremely low temperature in a living area where hydrogen can beutilized as an energy source and, at present, 243 K is an example ofsuch an extremely low temperature. The above elevated temperature region(T2) is a temperature which is higher than the above low-temperatureregion (T1) which is the hydrogen-absorbing temperature. The aboveelevated temperature region (T2) can be achieved by the use of a wasteheat (usually about 70 to 100° C.) generated at the fuel battery memberupon operation (i.e., corresponding to the hydrogen release process) ora heat from a heater exclusively therefor when the hydrogen storagemetal alloy is used, for example, as a tank for a fuel battery.

Although the method for absorbing and releasing hydrogen according tothe present invention is applicable to various kinds of a body-centeredcubic type hydrogen storage metal alloy, it is preferably applicable toV alloys, particularly, to hydrogen storage V metal alloys containingeach 0 to 95 at % of at least one or more elements selected from thegroup consisting of Ti, Cr, Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu, Ge,Ln (various lanthanoid metals), N, Ni, P and Si.

More preferably, when a method for absorbing and releasing hydrogenwhich comprises

absorbing hydrogen with an alloy wherein the stability of VH_(0.8) (orV(M)H_(0.8), i.e., a low-pressure

plateau region) is lowered, and

releasing hydrogen at an elevated temperature on a

final hydrogen release stage, is applied, it is possible to absorb anddesorb a much greater deal of hydrogen. With regard to a hydrogenrelease cycle, the desorption may be carried out at the temperaturewhich is same as that at hydrogen-absorption (the low temperature whichhas been mentioned until now; T1) during a part of the period but, atleast in the final stage of desorption, it is necessary to adjust to theabove-mentioned high temperature (T2) by means of heating so thathydrogen is sufficiently desorbed. Preferably, hydrogen at the abovehigh-pressure plateau part is desorbed at a relatively low temperature(which may be the same temperature as the above-mentioned T1) and, fortaking out the hydrogen from the above-mentioned low-temperature plateaupart at the final stage of the desorption of hydrogen, the alloy isheated to make the temperature high as mentioned above (T2) and todesorb the hydrogen.

As hereunder, the inventive effects of the method for absorbing andreleasing hydrogen according to the present invention will be morespecifically illustrated by citing the experiments conducted by thepresent inventors. Unless otherwise mentioned, the alloys used assamples were prepared in such a manner that the materials were weighedso as to bring the weight of ingot to 14 g, arc-melted in an argonatmosphere of 40 kPa and dissolved and stirred repeatedly three timesfor enhancing the uniformity and the resulting cast ingots per se wereused as samples or subjected to a heating treatment for homogenizationat 1473 K for 2 hours in an Ar atmosphere.

First, a measurement was carried out for V₇₀Zr_(0.5)Ti_(11.5)Cr₁₈ alloyswherein an large amount of V was contained, which have been brisklystudied at present. Before the measurement, a full deaeration wascarried out at the measuring temperature and then hydrogen absorptioncharacteristics were examined at a given measuring temperature. Theresults are shown in FIG. 6 (pressure vs composition isothermal curve:PCT line chart). It is understood from FIG. 6 that the lower themeasuring temperature, the lower the plateau pressure and the more thehydrogen storage amount.

The results of the measurement at 303 K (30° C.) and 323 K (50° C.) forhydrogen absorption and desorption characteristics of the aboveV₇₀Zr_(0.5)Ti_(11.5)Cr₁₈ alloy are shown in FIG. 7. When the hydrogenrelease characteristics at 303 K and 323 K are compared, it is notedthat a greater amount of hydrogen can be released when the operation iscarried out at the elevated temperature of 323 K. When the results ofFIG. 6 and FIG. 7 are summarized together, it has been noted that a muchgreater amount of hydrogen can be absorbed and released if hydrogen isabsorbed at low temperature and hydrogen is desorbed at hightemperature. Unlike the conventional hydrogen storage metal alloy havinga one-stage plateau (refer to FIG. 2), the hydrogen storage metal alloyhaving a two-stage plateau region does not show a clear decrease inamounts of absorbed and desorbed hydrogen even when operated at hightemperature because the low-pressure plateau region or the inclinedplateau region contributes to absorption and desorption of hydrogen whenoperation is carried out at high temperature as noted from the resultsas shown in FIG. 7, i.e., the hydrogen storage metal alloy begins toutilize a low-pressure plateau region.

When the PCT curves (FIG. 2 and FIG. 3) of the hydrogen storage metalalloy having a one-stage plateau mentioned in the paragraphs of RelatedArt of the Invention are checked once again, an increase in a hydrogenrelease curve by making the temperature high rarely occurs in the caseof a one-stage plateau alloy. Therefore, it is understood that elevationof the operation temperature in the hydrogen release process is quiteeffective for an increase in the amount of released hydrogen with regardto the hydrogen storage metal alloy having a two-stage plateau or aninclined plateau region.

Now, based upon the experimental results of FIG. 6 and FIG. 7 and byreferring to the PCT curve (conceptional chart) of v metal shown in FIG.1, a conceptional chart depicting an influence of the temperaturedifference in the PCT curve having a two-stage plateau has been preparedand is shown as FIG. 8. An increase in the amount of desorbed hydrogenis noted in the V₇₀Zr_(0.5)Ti_(11.5)Cr₁₈ alloy which has been examined.Then, a comparison has been made for the cases when operations werecarried out at a low temperature T1 and a high temperature T2. Althoughthere is nearly no difference in the amounts of absorbed and desorbedhydrogen between the two, it is likely that there occurs a bigdifference in the amounts of the residual hydrogen in the alloy. Now,when hydrogen was absorbed at low temperature T1 and released at highertemperature T2 than T1 (in other words, a differential temperaturemethod was applied), a conceptional chart is shown in FIG. 9 which showsan increase in the hydrogen capacity. Unlike the conventional hydrogenstorage metal alloy having a single plateau region, it is understoodfrom FIG. 9 that it is possible to increase the amounts of absorbed andreleased hydrogen in the case of a hydrogen storage metal alloy having atwo-stage plateau when such an alloy can be suitably designed andadjusted and a temperature may be elevated mostly at the taking stage ofhydrogen release process so as to lead to an increase in the operationtemperature with regard to the hydrogen storage metal alloy having aninclined plateau whereby a site related to a low-pressure plateau can becontributed to the hydrogen absorption/release. According to a principlewhich is different from the hydrogen storage metal alloy having aone-stage plateau alloy, the present inventors have found a possibilitythat an increase in amounts of released hydrogen can be achieved or ahigh capacity can be acquired for hydrogen storage metal alloy-equippedhydrogen tanks.

However, it has been well known as already mentioned in the above theparagraphs of Related Art of the Invention that it is impossible toincrease an amount of released hydrogen (i.e., to take out a sufficientamount of hydrogen from the low-pressure plateau region) by heating upto about 100° C. An increase in the hydrogen storage amount by adifferential temperature method has not been investigated yet. Thus, itcan be concluded that the V₇₀Zr_(0.5)Ti_(11.5)Cr₁₈ alloy of the presentinvention is capable of achieving an increase in the hydrogen releaseamount with elevating the temperature during the desorption stage,relying on a new principle different from the conventional V alloy. Thefact that such a conclusion can be applied to known V alloys havingdifferent compositions has been confirmed as follows:

The V₄₀Ti₂₅Cr₃₅ alloy which was reported in the aforementioned JP, A,10-110225 (having a spinodal decomposition tissue as a result of aheat-treatment at 1473 K for 2 hours) was subjected to an activatingtreatment followed by measurement for the first cycle and the secondcycle at 313 K (40° C.), and further subjected to a deaeration at roomtemperature for 5 hours or more, and then at 368 K (95° C.) for 3 hoursfollowed by measurement for the third cycle at 313 K. The PCT curves atthe second cycle and the third cycle are shown in FIG. 9. In the secondcycle wherein a usual hydrogen absorption/desorption process was carriedout, the amount of hydrogen which could be reversibly taken outtherefrom was about 2.4 mass % which was in the same degree as that inthe conventional report while in the third cycle wherein an elevatedtemperature process was introduced into the second cycle which was atthe same low temperature as in the conventional case the amount ofoccluded hydrogen slightly increased to 2.49 mass %.

Based upon these results, it is difficult to increase an amount ofstored hydrogen by a hydrogen desorption reaction from V(M)H_(0.8) withregard to a BCC type alloy containing about 40 at % of V. However, whena high-temperature cycle is carried out after the low-temperature cycle,the amount of occluded hydrogen increases. The efficacy of the alloyoperation method per se according to the present invention has beenconfirmed. Therefore, it is concluded that the amount of occludedhydrogen will increase if an improvement is carried out for thecomposition.

A V₃₀Cr₃₀Ti₄₀ alloy (having a spinodal decomposition tissue similarly tothe alloy of FIG. 6) wherein the amount of V was further reduced as analloy with an optimum composition to which the above cycle foreffectively utilizing hydrogen was applicable was measured for PCT curveup to 3 cycles at the constant temperature of 313 K. The results areshown in FIG. 1. The hydrogen storage amount obtained as a resultthereof is in a similar degree with one reported already.

Next, in order to confirm the effectiveness of the method according tothe present invention, a PCT curve measured at 313 K after deaeration at368 K for 2 hours as the fourth cycle and a PCT curve measured afterdeaeration at 363 K for 5 hours as the fifth cycle are shown in FIG. 12.It is confirmed that the amount of occluded hydrogen increases from 2.45mass % to 2.8 mass % when the method of the present invention isapplied. The important thing here is that an increase in the amount ofoccluded hydrogen is observed and the hydrogen absorption capacityamounts up to about 2.8 mass % for the V₃₀Cr₃₀Ti₄₀ alloy in spite of thefact that the V₃₀Cr₃₀Ti₄₀ alloy is not deaerated at room temperature andthe desorption time is shorter than in the case of the aforementionedV₄₀Ti₂₅Cr₃₅ alloy (being deaerated at room temperature before deaerationat high temperature). Therefore, according to the method of the presentinvention for absorbing and releasing hydrogen, it is possible to takeout the hydrogen more efficiently from the low-pressure region ascompared with the conventional operation at the constant temperaturewhereby it is noted that an effectively utilizable amount of occludedhydrogen can be significantly increased.

FIG. 13 shows a PCT absorption curve each of as cast and as heat-treatedat 1573 K for various retention time ranges V₃₅Ti₂₅Cr₄₀ alloys. Theresults show that the hydrogen-absorption characteristic is better inthe case where a heating treatment is not carried out at all or wherethe time for a heating treatment is as short as possible than the alloywhich is fully in the form of a spinodal decomposition. Based upon sucha finding, it is decided to permit the tissue of the alloys according tothe present invention so far as it is in a BCC mono phase without anyspinodal decomposition phase or with only a spinodal decomposition phaseunavoidably produced. The phrase “unavoidably produced” as used hereinrefers to shorter than 2 minutes which is slightly longer than -- inFIG. 13 and, when the time is as short as such, the alloy may be keptwithin a spinodal decomposition range. In the meanwhile, it will beapparent from the above illustration that, when the method of thepresent invention is applied to the alloy where the heating time is 2 to50 hours in FIG. 13, the corresponding increase in the hydrogen storageamount can be achieved.

It will be also apparent that, since the low-temperature plateau regionof the hydrogen storage metal alloy showing the two-stage plateau asmentioned above can be effectively utilized, the method of the presentinvention is applied to an alloy showing an inclined plateau whereby thelow-temperature region can be effectively utilized for hydrogenabsorption.

Then, a PCT curve measured at 368 K for a V_(x)Ti₃₀Cr_((70−x)) alloywherein the amount of V was varied is shown in FIG. 14. From the resultsof FIG. 14, it is noted that, at this temperature, hydrogen absorptiontook place up to 2.65 mass % and all of the occluded hydrogen,especially in the case of a V_(27.5)Ti₃₀Cr_(42.5) alloy, was desorbed.In the conventional alloy, only about one-half of the theoretical amountof hydrogen can be taken out; however, when hydrogen is taken out at 368K, the conclusion is that all of the occluded hydrogen in the sample canbe effectively utilized. The results when the method of the presentinvention was applied to this sample are shown in FIG. 15. Thus, thefirst cycle was carried out at the constant temperature in the samemanner as in the conventional case, then a deaeration was carried out at368 K in each of the second and third cycles before measurement and themeasurement was carried out at 313 K whereupon the amount of occludedhydrogen increased up to 2.8mass %. Accordingly, when hydrogen isabsorbed with a V_(27.5)Ti₃₀Cr_(42.5) alloy at 313 K and desorbed at 368K, the hydrogen can be utilized to the maximum extent. The results areshown in FIG. 16. The effectively utilized hydrogen amount is thedifference between the hydrogen storage amount at 7 Mpa in thehydrogen-absorbing process at 313 K and the residual hydrogen amount inthe alloy at 0.01 MPa in the hydrogen release process at 368 K.Accordingly, it is 2.7 mass %.

Similarly, the results of the present invention applied to amelt-prepared V₂₀Ti₃₅Cr₄₅ alloy are shown in FIG. 17.

In the drawing, there are shown PCT curves in the hydrogen releaseprocess for (1) the case (Δ) where hydrogen absorption and desorptionwas carried out at 368 K (90° C.), (2) a cycle (∇) wherein adifferential temperature method was introduced in such a manner thathydrogen desorption was carried out at 368 K and thereafter hydrogenabsorption and desorption was carried out at 313 K (40° C.), and (3) acycle () where hydrogen desorption was carried out at 368 K, hydrogenabsorption was carried out at 313 K and, during the hydrogen releaseprocess, heating was carried out up to 368 K with monitoring thedissociation pressure after hydrogen desorbing to an equilibriumhydrogen dissociation pressure of 0.05 MPa.

The curve shown by ∇ is the case where hydrogen desorption was carriedout at 368 K and then hydrogen absorption was carried out at 313 Kshowing a big storage amount. Accordingly, it is noted that thedifferential temperature method is effective.

The curve shown by  is the case where the operating temperature waselevated when the equilibrium dissociation pressure during the hydrogenrelease process arrived 0.05 MPa (temperature for each stage ismentioned in the drawing) and, as a result of heating, the dissociationpressure was controlled, the plateau region was flattened and theeffective amount of hydrogen was greatly increased. It is noted from thedrawing that the residual hydrogen amount in the alloy at 0.005 MPa isidentical with that in the desorption curve (Δ) obtained at 368 K.

Thus, it is noted that, when a differential temperature method is used,the amount of occluded hydrogen increases and, if the temperature iselevated during the hydrogen desorption, the effectively utilizablehydrogen amount increases.

Then, the results when the alloy operating method of the presentinvention, i.e., the differential temperature method, was applied to aV_(x)—Ti_((40−0.4x))—Cr_((60−0.6x)) cast alloy are shown in FIG. 18. Asshown herein the alloy wherein the level of V is brought to from 20 to60 at % exerts the hydrogen storage capacity of about 2.85 to 2.95 mass%. When this is compared with FIG. 4, it is noted that, when the methodof the present invention is applied, an increase in a hydrogen capacityto an extent of about 0.2 to 0.3 mass % is confirmed whereby theeffectiveness and usefulness of the present invention are noted.

Further, as mentioned already, when a V₄₀Ti₂₅Cr₃₅ alloy which wasreported to occlude about 2.4 mass % of hydrogen was subjected to anabsorption/desorption treatment by the present invention, a hydrogenstorage amount increased up to 2.49 mass %. The results where it waspartially substituted with Nb having a strong tendency of forming a BCCsolid solution are also shown in FIG. 15 while PCT curves of aV₄₀Ti₂₅Cr₃₅Nb₃ alloy as measured at the third and the fourth cycles andat 368 K are shown in FIG. 19. From the results, it is believed thathydrogen storage amounts increased by substitution with Nb and adissociation pressure of the low-pressure plateau region increased whenthe temperature was raised to 368 K. The effectively utilizable hydrogenamount is 2.7 mass %. It is noted that, as such, the hydrogen storageamount increases and the utilizable effective hydrogen amount increasesby the method of the present invention even in the known alloys bysubstituting with Nb.

FIG. 20 shows the results when the differential temperature method ofthe present invention was applied to a heat-treatedV_(x)—Ti_(37.5)—Cr_((62.5−x)) alloy exerting the hydrogen storage amountof as high as 2.8 mass % (refer to FIG. 5). Even in the alloys where thelevel of V is brought to as small as 5 to 7.5 atom %, a hydrogen storageamount of about 3.0 mass % is achieved when the present invention isapplied. When a comparison is made with the results of FIG. 5(absorption/desorption at the single temperature of 313 K in the samefashion as in the conventional method), an increase of about 0.2 mass %in the hydrogen capacity is noted upon application of the presentinvention whereby the effectiveness and usefulness of the presentinvention are noted. Especially in the case which is shown hereinabove,only the results are shown within such a temperature range where theutilization of waste heat is easy but it is also possible to form a highcapacity hydrogen storage metal alloy tank in a different manner when aheating apparatus is installed in the hydrogen storage metal alloy tankeither auxiliary or positively and a heating is carried out at the finalstage of the hydrogen release process.

As an example of the present invention, there is shown a case wherehydrogen was occluded at 313 K (40° C.) and desorbed at 368 K (95 ° C.).When the hydrogen-absorbing process is carried out at lower temperatureand the hydrogen desorption process is carried out at highertemperature, however, the effective amount of utilizable hydrogenfurther increases.

As mentioned hereinabove, when the hydrogen storage metal alloy of thepresent invention and the method for absorbing and releasing hydrogenusing the said hydrogen storage metal alloy are used, a good increase inthe hydrogen storage amount can be achieved even if the temperaturedifference between absorption and desorption of hydrogen is 40 to 100°C. which can be easily realized. Thus, by using a hydrogen storage metalalloy tank to which such a hydrogen storage metal alloy and a hydrogenabsorption/desorption method are applied, a hydrogen fuel battery with ahigh efficiency and a high capacity will be illustrated as hereunder.

FIG. 21 is a system flow chart showing a preferred embodiment of thehydrogen fuel battery according to the present invention. FIG. 22 is aschematic chart showing a mechanism of generation of electric power inthe fuel battery cell used in the hydrogen fuel battery of the presentinvention.

The constitution of the hydrogen fuel battery in the above embodiment isas shown in FIG. 21. The battery is mainly constituted from

a hydrogen fuel tank (4) installed with a hydrogen storage metal alloyin which the composition of constituent elements is suitably adjusted soas to make the occluded hydrogen desorbable in the low-pressure plateauregion by means of heating according to the present invention, said fueltank (4) being capable of supplying the hydrogen occluded in the saidhydrogen storage metal alloy to a fuel battery cell (1) which will bementioned later;

the said fuel battery cell (1) in which hydrogen supplied from the saidhydrogen fuel tank (4) is used as a fuel and the said hydrogen is madeto react with oxygen to change to water whereby the electric power canbe taken out while water is decomposed upon application of electricpower on the contrary whereby the hydrogen can be supplied to theaforementioned hydrogen fuel tank (4);

an inverter (2) in which a direct current electric power output from thesaid fuel battery cell (1) is converted to a predetermined alternatingcurrent electric power;

a heat exchanger (5) in which a heat exchange is carried out between theouter air as well as the discharged heat existing in a steam ofrelatively high temperature discharged from the said fuel battery cell(1) and the cold/warm water as a cooling/warming medium circulated in acooling/warming medium jacket installed at the outer circumference ofthe said hydrogen fuel tank (4); and

a controller (3) for conducting various control for elevating orlowering the temperature of the hydrogen storage metal alloy in the saidhydrogen fuel tank (4), mass control for pressure, flow rate,temperature, etc. with regard to hydrogen supplied to the said fuelbattery cell (1) and control for each of the above-mentioned members.

The said controller (3) is connected to pumps (P1 to P5),electromagnetic valves (V1 to V11), pressure valves (B1, B2), aflowmeter (FM) and temperature sensors (TS1 to TS3) installed on variouspiping as shown by broken lines in FIG. 21. LS in the drawing is a waterlevel sensor in a storage tank in which water produced is stored uponcooling the steam discharged from the fuel battery cell (1) by a heatexchanger (5).

As hereunder, the operation of the hydrogen fuel battery according tothe present embodiment will be illustrated. At first, a step of hydrogenabsorption with the hydrogen storage metal alloy in the above-mentionedhydrogen fuel tank (4) will be illustrated.

Firstly, the hydrogen which is to be absorbed with the hydrogen storagemetal alloy is supplied, as a starting material hydrogen (shown in FIG.21), into the hydrogen fuel tank (4) by connecting a high-pressurehydrogen cylinder to a hydrogen supplying outlet followed by opening thevalve (V1) whereupon the hydrogen storage metal alloy absorbs thehydrogen from the low-pressure plateau region to the high-pressureplateau region.

Simultaneously, the above-mentioned controller (3) releases the valves(V9 and V10) connected to the heat exchanger (5) and also makes the pump(P5) in an operating state whereby the outer air is sent into the heatexchanger to cool the above-mentioned cold/warm water with the outerair. At the same time, the hydrogen storage metal alloy is monitored forthe temperature with the above-mentioned temperature sensor (TS3) andthe circulation pump (P3) is appropriately operated so as to bring thetemperature (T1) of the said hydrogen storage metal alloy to 40° C. orlower whereby the above heat-exchanged cold/warm water is appropriatelypassed into the above-mentioned cooling/warming medium jacket to carryout the cooling of the hydrogen storage metal alloy. When thepredetermined amount of hydrogen is absorbed, the above-mentioned valve(V11) is closed and hydrogen absorption is finished.

When the fuel battery is operated to obtain the electric power aftersuch a hydrogen absorption is finished, the above-mentioned controller(3) opens the valve (V1), appropriately operates the above-mentionedpressure valve (B1) based upon the detection data from the flowmeter(FM), pressure sensor (PM) and temperature sensor (TS1) installed to thedownstream of the pressure valve (B1) so as to adjust a pressure andflow rate of hydrogen to be supplied to the fuel battery cell (1) fromthe hydrogen fuel tank (4) to a predetermined pressure, and controls thetemperature of hydrogen to be supplied with appropriately passing theabove-mentioned cold/warm water through the above-mentionedcooling/warming medium jacket. Simultaneously, the controller (3)operates the pump (P1) so that the oxygen in the outer air is sent intothe above-mentioned fuel battery cell (1).

Each operation of the members including the controller (3) beforegenerating electric power by the fuel battery cell can be carried out bymeans of a storage battery (not shown) installed in the said hydrogenfuel battery. As a result of supplying the hydrogen and the oxygen(outer air) to the fuel battery cell (1) as above, direct current isobtained in the said fuel battery cell (1), as shown in FIG. 22, withthe reaction which is reverse to the production of hydrogen and oxygenvia electrolysis of water by application of direct current to water towhich an electrolyte has been added. Therefore, hydrogen moleculessupplied from the hydrogen fuel tank (4) become hydrogen ions byreleasing electrons at a hydrogen electrode and the resulting electronsmove to a positive electrode side whereupon electric power is generated.

Such hydrogen ions move to the positive electrode side in anelectrolyte, receive electrons at the positive electrode to return tohydrogen atoms and simultaneously react with oxygen contained in theabove-mentioned supplied outer air to form water (steam). With regard toan exhaust gas containing the steam of relatively high temperature(around 70 to 90° C.) due to heat liberated in the exothermic reactionto water, when the heat of the exhaust gas is utilized to heat theabove-mentioned cold/warm water, the said controller (3) opens thevalves (V5, V7) (naturally, the valves V9, V10 and V6 are in a closedstate) to introduce the exhaust gas into the heat exchanger (5) so thatthe heat would be exchanged. The exhaust gas cooled by the said heatexchange is discharged to outer air via a storage tank while the waterproduced by the said cooling is stored in a storage tank. When such aheat exchange is not needed, the valves (V5 and V7) are in a closedstate and, after the valve V6 is opened and the above-mentioned exhaustgas is exposed to air in the storage tank whereupon the steam isappropriately removed, it is discharged to outer air. It goes withoutsaying that, during such an operation stage, the valve (V4) is in anopened state.

In the starting stage of electric power generation as such, the hydrogenwhich is supplied from the above-mentioned hydrogen fuel tank (4)originates in the high-pressure plateau region of the above-mentionedhydrogen storage metal alloy and therefore the temperature of thehydrogen storage metal alloy is controlled to a temperature nearlyequivalent to that during the above-mentioned hydrogen absorption.However, when release of hydrogen continues and the supplied hydrogenpressure lowers by a decrease in the hydrogen release from thehigh-pressure plateau region of the said hydrogen storage metal alloy,the above-mentioned controller (3) conducts its valve control asmentioned above for the heat exchange in the heat exchanger (5) andsimultaneously the cold/warm water heated by the heat exchanger ispassed to the hydrogen fuel tank (4) by making the circulation pump (P3)in an operating state whereupon heating of the hydrogen storage metalalloy is started.

As a result of heating as such, the temperature of the above-mentionedhydrogen storage metal alloy is elevated and as aforementioned theoccluded hydrogen in the lower region of the inclined plateau or in thelow-pressure plateau region is desorbed. Such a desorbed hydrogen issupplied to the fuel battery cell (1) so that generation of electricpower is continuously carried out whereupon the electric powergenerating capacity of the hydrogen fuel battery can be significantlyimproved.

With regard to the heating temperature (T2) of such a hydrogen storagemetal alloy, since water is used as a cooling/warming medium in thisexample, its upper limit is around 90° C. but the present invention isnot limited to. Such a hydrogen storage metal alloy may be heated with aheater or the like to bring it to a higher temperature. Further, in thisexample, temperature upon hydrogen absorption is made not higher than40° C. which is practical by means of cooling due to heat release with aheat exchange to the outer air but the present invention is not limitedto. Such a cooling may be carried out by installment of a coolingapparatus or by using as the cooling/warming medium a cooling mediumsuch as flon or ammonia together with a heat pump in which a heatexchange is carried out by compression and expansion of such a coolingmedium. Furthermore, in place of such a heat pump, it is also possibleto carry out both cooling and heating by the use of a Peltier element.

It is preferred to use a heat exchanger (5) as mentioned above sincemuch electric power is not necessary for heating and cooling, theresulting electric power from the said hydrogen fuel battery can beincreased greatly and the efficiency of the hydrogen fuel battery can beimproved although the present invention is not limited thereto.

At a next step, when release of hydrogen as such is finished and freshhydrogen is to be stored, there is a method, in addition to the means ofsupplying the starting material hydrogen to the hydrogen fuel tank (4)as mentioned above, where electric power is applied to theabove-mentioned fuel battery cell (1) and hydrogen produced bydecomposition of water is stored.

The above means will be illustrated as follows:

At first, a predetermined direct current is applied to theabove-mentioned fuel battery cell (1),

the pump (P4) is operated under the condition where the valve (V4) isclosed,

an outer air is passed into the water which is stored in the storagetank via the above-mentioned generation of electric power so as tocontain steam and

the air containing the said steam is supplied into the fuel battery cell(1) via the valve (V6).

As a result, water is adhered onto the surface of the positive electrodeside in the said fuel battery cell (1), the said adhered water iselectrolyzed to give oxygen, air containing the said oxygen isdischarged outside the fuel battery cell (1) while hydrogen producedsimultaneously by the said electrolysis becomes a hydrogen ion viaremoval of electron at the above-mentioned positive electrode side, thesaid hydrogen ion moves in the electrolyte in the same manner as in theabove-mentioned electric power generation stage to arrive at thehydrogen electrode side, then receives an electron at the said hydrogenelectrode side to form a hydrogen molecule followed by release from thesaid hydrogen electrode.

Hydrogen released as such is compressed by a pump (P2) where the valve(V2) is in an opened state and supplied to the pressure valve (B2). Thehydrogen brought to a predetermined pressure via the said pressure valve(B2) is supplied into the hydrogen fuel tank (4) and is absorbed withthe above-mentioned hydrogen storage metal alloy. At that time, in thesame manner as in the above-mentioned hydrogen supply from the hydrogencylinder, the above-mentioned controller (3) adjusts the temperature ofthe said hydrogen storage metal alloy to 40° C. or lower so thathydrogen can be repeatedly absorbed and released. Thus, the saidcontroller (3) can lower the temperature of the hydrogen storage metalalloy during the hydrogen absorption and elevate the temperature ofhydrogen storage metal alloy during the hydrogen release, particularlyat the final stage of hydrogen release, whereby an amount of hydrogensuppliable to the fuel battery cell can be increased and much moregeneration of electric power becomes available.

Symbols used in the drawings have the following meanings: 1 is a fuelbattery cell; 2 is an inverter; 3 is a controller (controlling member) ;4 is a hydrogen fuel tank (hydrogen storage tank); and 5 is a heatexchanger (temperature adjusting means).

What is claimed is:
 1. A hydrogen storage metal alloy which has as itsmain phase a body-centered cubic structure-type phase exerting atwo-stage or inclined plateau characteristic in a hydrogen storageamount vs hydrogen pressure relation, in which the composition ratio ofconstituent metals for the alloy is adjusted to an appropriate range inorder to reduce the stability of the hydrogen occluded in the alloyduring the low-pressure plateau region or the lower plateau region ofthe inclined plateau such that an alloy temperature (T2) during at leasta period in a hydrogen release process can be brought to higher than analloy temperature (T1) in a hydrogen-absorption process (T2>T1) wherebyat least part of the occluded hydrogen will be made desorbable duringthe low-pressure plateau region in the above-mentioned two-stage plateauor the lower plateau region of the inclined plateau, wherein thehydrogen storage metal alloy is an alloy having not only a suitablyadjusted composition to reduce the stability of the occluded hydrogenbut also a fundamental composition of the formula:V_((a−b))M2₂Ti_((41−4a+b))Cr_((59−6a−b−c))M_(c) wherein 0≦a≦70 at %,−10≦b≦10+c, 0≦c, 0≦d≦a, M is at least one or more members selected fromthe group consisting of Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu, Ge, Ln(various lanthanoid metals), N, Ni, P and Si, and M2 is at least one ormore members selected from the group consisting of Mo, Nb, Ta, W, Mn, Feand Al.
 2. The hydrogen storage metal alloy according to claim 1,wherein the alloy temperature (T1) during the hydrogen-absorbing processis brought to a range of from the extremely low temperature in theliving areas on the earth to 373 K.
 3. The hydrogen storage metal alloyaccording to claim 1, wherein the tissue structure of theabove-mentioned suitably adjusted hydrogen storage metal alloy is of abody-centered cubic structure mono phase without any spinodaldecomposition phase or has a body-centered cubic structure together withonly a minimum spinodal decomposition phase which is unavoidablyproduced.
 4. A method for absorbing and releasing hydrogen using ahydrogen storage metal alloy which comprises: applying repeatedlyhydrogen pressurization and depressurization to the hydrogen storagemetal alloy of a body-centered cubic structure-type phase exerting atwo-stage or inclined plateau characteristic in a hydrogen storageamount vs hydrogen pressure relation in an appropriate fashion to absorband release hydrogen, and at least at one stage during the release ofhydrogen, making the temperature (T2) of the above-mentioned hydrogenstorage metal alloy higher than the temperature (T1) of the hydrogenstorage metal alloy during the hydrogen absorption process (T2>T1)wherein the hydrogen storage metal alloy is an alloy having not only asuitably adjusted composition to reduce the stability of the occludedhydrogen but also (1) a fundamental composition of the formula:V_((a−b))M2₂Ti_((41−0.4a+b))Cr_((59−0.6a−b−c))M_(c)  wherein 0≦a≦70 at%, −10≦b≦10+c, 0≦c, 0≦d≦a, M is at least one or more members selectedfrom the group consisting of Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu,Ge, Ln (various lanthanoid metals), N, Ni, P and Si, and M2 is at leastone or more members selected from the group consisting of Mo, Nb, Ta, W,Mn, Fe and Al, or (2) a fundamental composition of the formula:V_((a+b))M2_(d)Ti_((41−0.4a+b))M_(c)  wherein 0≦a≦70 at %, −10≦b≦10+c,0≦c, 0≦d≦a, M is at least one or more members selected from the groupconsisting of Nb, Mo, Ta, W, Mn, Fe, al, B, C, Co, Cu, Ge, Ln (variouslanthanoid metals), N, Ni, P and Si, and M2 is at least one or moremembers selected from the group consisting of Mo, Nb, Ta, W, Fe and Al.5. The method for absorbing and releasing hydrogen according to claim 4,wherein the tissue structure of the above-mentioned suitably adjustedhydrogen storage metal alloy is of a body-centered cubic structure monophase without any spinodal decomposition phase or has a body-centeredcubic structure together with only a minimum spinodal decompositionphase which is unavoidably produced.
 6. The method for absorbing andreleasing hydrogen according to claim 4, wherein the alloy temperature(T1) during the above hydrogen-absorbing process is within a range offrom the extremely low temperature in the living areas on the earth to373 K.
 7. The method for absorbing and releasing hydrogen according toclaim 6, wherein the composition ratio of the constituent metals for thealloy is adjusted to an appropriate range in order to reduce thestability of the hydrogen occluded in the alloy during the low-pressureplateau region or the lower plateau region of the inclined plateau suchthat the temperature of the said alloy can be brought to the above hightemperature (T2) whereby at least part of the occluded hydrogen will bemade desorbable during the low-pressure plateau region in theabove-mentioned two-stage plateau or the lower plateau region of theinclined plateau.
 8. The method for absorbing and releasing hydrogenaccording to claim 4, wherein the composition ratio of the constituentmetals for the alloy is adjusted to an appropriate range in order toreduce the stability of the hydrogen occluded in the alloy during thelow-pressure plateau region or the lower plateau region of the inclinedplateau such that the temperature of the said alloy can be brought tothe above high temperature (T2) whereby at least part of the occludedhydrogen will be made desorbable during the low-pressure plateau regionin the above-mentioned two-stage plateau or the lower plateau region ofthe inclined plateau.
 9. The method for absorbing and releasing hydrogenaccording to claim 4, wherein the hydrogen storage metal alloy is analloy having not only a suitably adjusted composition to reduce thestability of the occluded hydrogen but also a fundamental composition ofthe formula: V_((a+b))M2_(d)Ti_((41−0.4a+b))M_(c) wherein 0≦a≦70 at %,−10≦b≦10+c, 0≦c, 0≦d≦a, M is at least one or more members selected fromthe group consisting of Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu, Ge, Ln(various lanthanoid metals), N, Ni, P and Si, and M2 is at least one ormore members selected from the group consisting of Mo, Nb, Ta, W, Fe andAl.
 10. The method for absorbing and releasing hydrogen according toclaim 9, wherein the tissue structure of the above-mentioned suitablyadjusted hydrogen storage metal alloy is of a body-centered cubicstructure mono phase without any spinodal decomposition phase or has abody-centered cubic structure together with only a minimum spinodaldecomposition phase which is unavoidably produced.
 11. The method forabsorbing and releasing hydrogen according to claim 4, wherein thehydrogen storage metal alloy is an alloy having not only a suitablyadjusted composition to reduce the stability of the occluded hydrogenbut also a fundamental composition of the formula:V_((a−b))M2_(d)Ti_((41−0.4a+b))Cr_((59−0.6a−b−c))M_(c) wherein 0≦a≦70 at%, −10≦b≦10+c, 0≦d≦a, M is at least one or more members selected fromthe group consisting of Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu, Ge, Ln(various lanthanoid metals), N, Ni, P and Si, and M2 is at least one ormore members selected from the group consisting of Mo, Nb, Ta, W, Mn, Feand Al.
 12. The method for absorbing and releasing hydrogen according toclaim 11, wherein the tissue structure of the above-mentioned suitablyadjusted hydrogen storage metal alloy is of a body-centered cubicstructure mono phase without any spinodal decomposition phase or has abody-centered cubic structure together with only a minimum spinodaldecomposition phase which is unavoidably produced.
 13. A hydrogen fuelbattery equipped with: a hydrogen storage tank including a hydrogenstorage metal alloy, a temperature controlling means whereby the abovehydrogen storage metal alloy is directly heated or cooled or theatmospheric temperature of the said hydrogen storage metal alloy israised or cooled, a fuel battery cell in which hydrogen supplied fromthe said hydrogen storage tank can be subjected to a chemical change tooutput an electrical power, and a controller where a control is done insuch a manner that, with regard to the temperature (T1) of the abovehydrogen storage metal alloy during the stage of hydrogen absorption,the temperature of the said alloy during at least one period during therelease of hydrogen is made higher (T2) than the temperature (T1)thereof during the above hydrogen-absorbing process.
 14. The hydrogenfuel battery according to claim 13, wherein the aforementionedcontroller is capable of approximately controlling a pressure,temperature and flow rate of the hydrogen gas supplied from theabove-mentioned hydrogen storage tank to the above-mentioned fuelbattery cell.
 15. The hydrogen fuel battery according to claim 14,wherein the above-mentioned temperature controlling means is arranged soas to enable the heat discharged from the above-mentioned fuel batterycell or the exhaust gas discharged from the said fuel battery cell tothe utilized for the above-mentioned heating.
 16. The hydrogen fuelbattery according to claim 13, wherein the above-mentioned temperaturecontrolling means is arranged so as to enable the heat discharged fromthe above-mentioned fuel battery cell or the exhaust gas discharged fromthe said fuel battery cell to be utilized for the above-mentionedheating.
 17. The hydrogen fuel battery according to claim 13, whereinthe hydrogen storage metal alloy has as its main phase a body-centeredcubic structure-type phase exerting a two-stage or inclined plateaucharacteristic in a hydrogen storage amount vs hydrogen pressurerelation, in which the composition ratio of constituent metals for thealloy is adjusted to an appropriate range in order to reduce thestability of the hydrogen occluded in the alloy during the low-pressureplateau region or the lower plateau region of the inclined plateau suchthat an alloy temperature (T2) during at least a period in a hydrogenrelease process can be brought to higher than an alloy temperature (T1)in a hydrogen-absorption process (T2>T1) whereby at least part of theoccluded hydrogen will be made desorbable during the low-pressureplateau region in the above-mentioned two-stage plateau or the lowerplateau region of the inclined plateau.
 18. The hydrogen fuel batteryaccording to claim 17, wherein the alloy temperature (T1) during thehydrogen-absorbing process is brought to a range of from the extremelylow temperature in the living areas on the earth to 373 K.
 19. Thehydrogen fuel battery according to claim 18, wherein the hydrogenstorage metal alloy is a V alloy not only having a suitably adjustedcomposition to reduce the stability of the occluded hydrogen but alsocontaining 0 to 95 at % of at least one or more members selected fromthe group consisting of Nb, Ta, W, Mo, Ti, Cr, Mn, Fe, Al, B, Co, Cu,Ge, Ni and Si.
 20. The hydrogen fuel battery according to claim 19,wherein the hydrogen storage metal alloy is an alloy having not only asuitably adjusted composition to reduce the stability of the occludedhydrogen but also a fundamental composition of the formula:V_(a)Ti_((41−0.41+b))Cr_((59−0.6a−b)) wherein 0≦a≦70 at % and −10≦b≦10at %.
 21. The hydrogen fuel battery according to claim 20, wherein thetissue structure of the above-mentioned suitably adjusted hydrogenstorage metal alloy is of a body-centered cubic structure mono phasewithout any spinodal decomposition phase or has a body-centered cubicstructure together with only a minimum spinodal decomposition phasewhich is unavoidably produced.
 22. The hydrogen fuel battery accordingto claim 19, wherein the hydrogen storage metal alloy is an alloy havingnot only a suitably adjusted composition to reduce the stability of theoccluded hydrogen but also a fundamental composition of the formula:V_((a−b))M2_(d)Ti_((41−0.4a+b))Cr_((59−0.6−b−))M_(c) wherein 0≦a≦70 at%, −10≦b≦10+c, 0≦c, 0≦d≦a, M is at least one or more members selectedfrom the group consisting of Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu,Ge, Ln (various lanthanoid metals), N, Ni, P and Si, and M2 is at leastone or more members selected from the group consisting of Mo, Nb, Ta, W,Mn, Fe and Al.
 23. The hydrogen fuel battery according to claim 22,wherein the tissue structure of the above-mentioned suitably adjustedhydrogen storage metal alloy is of a body-centered cubic structure monophase without any spinodal decomposition phase or has a body-centeredcubic structure together with only a minimum spinodal decompositionphase which is unavoidably produced.
 24. The hydrogen fuel batteryaccording to claim 19, wherein the tissue structure of theabove-mentioned suitably adjusted hydrogen storage metal alloy is of abody-centered cubic structure mono phase without any spinodaldecomposition phase or has a body-centered cubic structure together withonly a minimum spinodal decomposition phase which is unavoidablyproduced.
 25. The hydrogen fuel battery according to claim 19, whereinthe hydrogen storage metal alloy is an alloy having not only a suitablyadjusted composition to reduce the stability of the occluded hydrogenbut also a fundamental composition of the formula:V_((a+b))M2_(d)Ti_((41−0.4a+b))M_(c) wherein 0≦a≦70 at %, −10≦b≦10+c,)≦d≦a, M is at least one or more members selected from the groupconsisting of Nb, Mo, Ta, W, Mn, Fe, Al, B, C, Co, Cu, Ge, Ln (variouslanthanoid metals), N, Ni, P and Si, and M2 is at least one or moremembers selected from the group consisting of Mo, Nb, Ta, W, Fe and Al.26. The hydrogen fuel battery according to claim 25, wherein the tissuestructure of the above-mentioned suitably adjusted hydrogen storagemetal alloy is of a body-centered cubic structure mono phase without anyspinodal decomposition phase or has a body-centered cubic structuretogether with only a minimum spinodal decomposition phase which isunavoidably produced.